Thermal energy storage systems and methods

ABSTRACT

A thermal energy storage apparatus is disclosed. The thermal energy storage apparatus has a phase change medium, an inner header having at least one inner feed port, and an outer header having at least one outer feed port and fluidically coupled to the inner header. The inner header and the outer header are configured to be substantially immersed in the phase change medium. Related methods of constructing and controlling a thermal energy storage system are also disclosed. A thermal energy power system utilizing a thermal energy storage apparatus is further disclosed, as is a heat exchanger for the thermal energy storage system.

RELATED APPLICATIONS

This application claims priority to U.S. provisional patent application 60/939,426 which was filed on May 22, 2007. U.S. provisional patent application 60/939,426 is hereby incorporated by reference in its entirety.

FIELD

The claimed invention generally relates to energy storage and, more particularly, to thermal energy storage systems and methods thereof.

BACKGROUND

Worldwide, there are ever-growing demands for electricity due to increasing populations, technology advancements requiring the use of electricity, and the proliferation of such technology to more and more countries around the world. At the same time, there is an increasing push to harness reusable sources of energy to help meet these increasing electricity demands and offset and/or replace traditional carbon-based generators which continue to deplete natural resources around the world.

Many solutions have been developed to collect and take advantage of reusable sources of energy, such as solar cells, solar mirror arrays, and wind turbines. Solar cells produce direct current energy from sunlight using semiconductor technology. Solar mirror arrays focus sunlight on a receiver pipe containing a heat transfer fluid which absorbs the sun's radiant heat energy. This heated transfer fluid is then pumped to a turbine which heats water to produce steam, thereby driving the turbine and generating electricity. Wind turbines use one or more airfoils to transfer wind energy into rotational energy which spins a rotor coupled to an electric generator, thereby producing electricity when the wind is blowing. All three solutions produce electricity when their associated reusable power source (sun or wind) is available, and many communities have benefited from these clean and reusable forms of power.

Unfortunately, when the sun or wind is not available, such solutions are not producing any power. In the case of solar solutions, non-reusable energy solutions are often turned-to overnight. Similar issues arise for wind turbines during calm weather. Therefore, some form of energy storage is needed to store excess energy from the reusable power sources during power generation times to support energy demands when the reusable power source is unavailable or unable to meet peak demands for energy.

Solar mirror arrays generate and transfer heat as an inherent part of their operation. Solar cells and wind turbines which typically generate electricity can also selectively be used to drive heaters to generate heat and/or transfer heat from windings to a heat transfer fluid. Several solutions have been developed to store heat from these renewable energy sources for use in non-energy-generating times.

FIG. 1 illustrates a two-tank direct energy storage system. Heat transfer fluid is heated by mirrors in a solar field 30 and stored in a hot oil tank 32. The heat transfer fluid is then pumped through a steam generator 34 as needed to generate steam and power a turbine 36 to meet energy demands. Even if the solar field 30 is not producing newly heated heat transfer fluid for the hot oil tank 32, the hot oil tank 32 has a certain capacity to provide stored hot transfer fluid to the steam generator 34 for power generation. After passing though the steam generator 34, the cooled heat transfer fluid is then pumped into and stored in a cold oil tank 38. When the solar field 30 is active, cooled heat transfer fluid is pumped from the cold oil tank 38, through the solar field to be heated-up, and back to the hot oil tank 32 where the process can begin again. While the two-tank direct energy storage system of FIG. 1 helps to store energy for non-generation times, it is unfortunately complex, requires two expensive tanks, and is limited in the amount energy it can store due to limitations in the heat storage capacity of the heat transfer fluid.

FIG. 2 illustrates a two-tank indirect energy storage system. Relatively cold molten salt is pumped from a cold salt tank 40 out to a heat exchanger 42 where it is heated by proximity to counter-current running hot heat transfer fluid from the solar field 44. The newly-heated molten salt is then pumped from the heat exchanger 42 into a hot salt tank 46 where it is stored until needed. When energy needs to be reclaimed from the hot salt tank 46, the hot molten salt is pumped out of the hot salt tank 46 and to a turbine system 48 whereby the heat from the hot molten salt is used to generate steam to drive the turbine system 48. Relatively cold molten salt exits the turbine system 48 and is pumped back into the cold salt tank 40. Alternatively, the hot molten salt from the hot salt tank 46 may be pumped out of the hot salt tank 46 and back through the heat exchanger 42 to heat the heat transfer fluid from the solar field 44 before being pumped back into the cold salt tank 40. In this alternate setup, the reheated heat transfer fluid would then be pumped through the turbine system before being recirculated to the solar field. Taking advantage of the heat storage capacities of salt in this indirect two-tank system, more energy may be stored than in the direct system. Unfortunately, this system still requires two expensive tanks. Furthermore, the system of FIG. 2 will be subjected-to complexities and issues arising from the need to pump and transport molten salt. The system may have the need to keep the salt molten at all times and therefore may require the addition of heaters not powered by the solar field. If the salt is allowed to solidify within the transport pipes, the natural expansion of the salt when transitioning to a solid state may cause stress cracks in the pipes. Furthermore, if the salt is allowed to solidify, the system may take an undesirable amount of time to come on-line as it waits for the salt to liquefy to become pumpable. Corrosion is also an issue when pumping molten salt.

FIG. 3 illustrates a single-tank thermocline energy storage system. The thermocline tank 50 holds a hot molten salt on the top of the tank 50 and a relatively cool molten salt in the bottom of the tank 50. When the solar field 52 is active, a hot heat transfer fluid is pumped from the solar field to a heat exchanger 54. The relatively cool molten salt is pumped out of the bottom of the thermocline tank 50 out to the heat exchanger 54 where it is heated by proximity to the hot heat transfer fluid from the solar field. The heated molten salt is then returned to the top of the thermocline tank 50. When the solar field 52 is not active, the flow to and from the thermocline tank 50 is reversed. Heated molten salt is pumped out of the top of the thermocline tank 50 to the heat exchanger 54, where it transfers its heat to the heat transfer fluid. The heat transfer fluid is pumped to a turbine system 56 for generating electricity. The molten salt which gave up some of its heat in the heat exchanger 54 is then returned to the bottom of the thermocline tank 50. While this system takes advantage of a vertical temperature gradient within the thermocline tank to move down to a single tank, the tank itself may still be expensive when properly sized for industrial and/or community demands, and the system continues to have the corrosion and solidification concerns mentioned above when pumping molten salt.

Therefore, there is a need for a thermal energy storage system which can take advantage of the high energy storage capacities of phase change media, such as salts, while avoiding corrosion and solidification issues in an inexpensive, easy-to-construct, control, and maintain fashion.

SUMMARY

A thermal energy storage apparatus is disclosed. The thermal energy storage apparatus has a phase change medium, an inner header having at least one inner feed port, and an outer header having at least one outer feed port and fluidically coupled to the inner header. The inner header and the outer header are configured to be substantially immersed in the phase change medium.

A thermal energy power system is also disclosed. The thermal energy power system has a phase change medium, an inner header, an outer header, and a collection header. The thermal energy power system also has one or more inner tubes coupled between the inner header and the collection header. The thermal energy power system further has one or more outer tubes coupled between the outer header and the collection header, wherein the inner header is fluidically coupled to the outer header via the one or more inner tubes, the collection header, and the one or more outer tubes. The thermal energy power system also has a brick structure configured to contain the phase change medium such that the inner header and the outer header are substantially immersed in the phase change medium and wherein the bricks are configured to have a cooling zone which encourages the phase change medium to solidify in gaps defined by the bricks. The thermal energy power system also has a base which supports the brick structure, a pump, a renewable heat collector, and a turbine plant. The inner header and the outer header are reversibly connected in a series closed loop with the pump, the renewable heat source, and the turbine plant. The closed loop carries a thermal fluid.

A method of constructing a thermal energy storage system is also disclosed. A base is formed. At least one heat exchange system is substantially aligned over the base, the at least one heat exchange system comprising an inner header and an outer header. A brick wall is dry-laid substantially on the base to surround the at least one heat exchange system. An area defined by the base and the brick wall is filled with a phase change medium such that the phase change medium substantially covers the at least one heat exchange system.

A method of controlling a thermal energy storage system is also disclosed. When a renewable heat source is available: i) the renewable heat source is thermally and fluidically coupled to an inner header of a heat exchange system which is substantially immersed in a phase change medium and which is further coupled to an outer header of the heat exchange system which is also substantially immersed in the phase change medium; and ii) the outer header is thermally and fluidically coupled to a turbine plant and then back to the renewable heat source in a closed-loop heating mode which provides a remaining renewable energy source heat to the turbine plant. When the renewable heat source is not available: i) the renewable heat source is thermally and fluidically coupled to the outer header; and ii) the inner header is thermally and fluidically coupled to the turbine plant and then back to the renewable heat source in a closed-loop cooling mode which provides a stored heat to the turbine plant. A heat exchanger for a thermal energy storage system is also disclosed. The heat exchanger has

an inner header having at least one inner feedport. The heat exchanger also has an outer header having at least one outer feedport and fluidically coupled to the inner header. The inner and outer feedports are configured to enable a heat transfer fluid to reversibly flow from the inner header to the outer header when the inner header and the outer header are substantially immersed in a phase change medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art embodiment of a direct two-tank thermal energy storage system.

FIG. 2 illustrates a prior art embodiment of an indirect two-tank thermal energy storage system.

FIG. 3 illustrates a prior art embodiment of a single tank thermocline energy storage system.

FIG. 4 schematically illustrates a side cross-sectional view of one embodiment of a heat exchanger for use in an energy storage system.

FIG. 5 schematically illustrates a top view of the embodied heat exchanger of FIG. 4.

FIG. 6 schematically illustrates a side cross-sectional view of another embodiment of a heat exchanger for use in an energy storage system.

FIG. 7 schematically illustrates a side cross-sectional view of another embodiment of a heat exchanger for use in an energy storage system.

FIG. 8 schematically illustrates a side cross-sectional view of a further embodiment of a heat exchanger for use in an energy storage system.

FIG. 9 schematically illustrates one embodiment of a thermal energy storage apparatus.

FIG. 10A schematically illustrates another embodiment of a thermal energy storage apparatus.

FIG. 10B schematically illustrates a further embodiment of a thermal energy storage apparatus.

FIG. 11 illustrates an embodiment of a method for constructing a thermal energy storage system.

FIG. 12A schematically illustrates a side cross-sectional view of another embodiment of a thermal energy storage system.

FIG. 12B schematically illustrates a cross-sectional view of the embodied thermal energy storage system shown in FIG. 12A taken along lines 2-2.

FIG. 12C schematically illustrates a cross-sectional view of the embodied thermal energy storage system shown in FIG. 12A taken along lines 3-3.

FIG. 12D schematically illustrates flow through the embodied thermal energy storage system of FIG. 12A during heating to store energy.

FIG. 12E schematically illustrates flow through the embodied thermal energy storage system of FIG. 12A during cooling to deliver energy.

FIG. 13 schematically illustrates an embodiment of a thermal energy power system.

FIG. 14 schematically illustrates flow through the embodied thermal energy power system of FIG. 13 during a heating mode.

FIG. 15 schematically illustrates flow through the embodied thermal energy power system of FIG. 13 during a cooling mode.

FIG. 16 illustrates an embodiment of a method for controlling a thermal energy storage system.

It will be appreciated that for purposes of clarity and where deemed appropriate, reference numerals have been repeated in the figures to indicate corresponding features, and that the various elements in the drawings have not necessarily been drawn to scale in order to better show the features.

DETAILED DESCRIPTION

FIG. 4 schematically illustrates a side cross-sectional view of one embodiment of a heat exchanger 58 for use in an energy storage system. The heat exchanger 58 has an inner header 60 with an inner feedport 62. The heat exchanger 58 also has an outer header 64 with an outer feedport 66. The inner feedport 62 and the outer feedport 66 do not have to project out from the inner and outer headers 60, 64. The inner and outer feedports 62, 66 may optionally be openings which provide access for fluid delivery via external piping which can be attached to inner and outer feedports 62, 66. Such external piping may enter vertically, horizontally, or at any desired angle. The outer header 64 is fluidically coupled to the inner header 60, in this embodiment via outer tubes 68, 70 and inner tube 72. Other embodiments may have differing numbers of inner tubes and/or outer tubes. In this embodiment, the inner header 60 and the outer header 64 have a circular cross-sectional shape. In other embodiments, the inner header and the outer header may have other cross-sectional shapes, such as, but not limited to oval, square, triangular, and hexagonal. The inner header 60 and the outer header 64 do not have to have the same cross-sectional shape or size. Certain cross-sectional shapes may provide more or less surface area for heat transfer or may assist with ease of manufacturing and may be chosen to fit certain heat transfer and assembly goals by those skilled in the art depending on the embodiment.

In this embodiment, the inner header 60 and the outer header 64 lie in substantially the same plane. In other embodiments, the inner header 60 may be on a lower plane than the outer header 64 or visa versa. Furthermore, in this embodiment, the inner header 60 is centered within the outer header 64. In other embodiments, the inner header 60 may be off-center in comparison with the outer header 64.

The inner header 60 and the outer header 64 may be constructed of a variety of materials, for example, but not limited to plain carbon steels; alloy steels, manganese, silicon, silicon-manganese, nickel, nickel-chromium, molybdenum, nickel-molybdenum, chromium, chromium-molybdenum, chromium-molybdenum-cobalt, silicon-molybdenum, manganese-silicon-molybdenum, nickel-chromium-molybdenum, silicon-chromium-molybdenum, manganese-chromium-molybdenum, manganese-silicon-chromium-molybdenum, vanadium, chromium-vanadium, silicon-chromium-vanadium, manganese-silicon-chromium-vanadium, chromium-vanadium-molybdenum, manganese-silicon-chromium-vanadium-molybdenum, chromium-tungsten, chromium-tungsten-molybdenum, chromium-tungsten-vanadium, chromium-vanadium-tungsten-molybdenum, chromium-vanadium-tungsten-cobalt, chromium-vanadium-tungsten-molybdenum-cobalt; stainless steels, austenitic, ferritic, martensitic, duplex, precipitation-hardening, superaustenitic, superferritic; nickel alloys, nickel-chromium-iron, nickel-chromium-iron-aluminum, nickel-chromium-iron-aluminum-titanium, nickel-chromium-iron-aluminum-titanium-niobium, nickel-chromium-iron-cobalt-molybdenum, nickel-chromium-iron-niobium, nickel-chromium-iron-molybdenum-niobium, nickel-chromium-iron-molybdenum-niobium-titanium-aluminum, nickel-chromium-molybdenum-iron-tungsten, nickel-chromium-iron-molybdenum-copper-titanium, nickel-chromium-iron-molybdenum-titanium, nickel-iron-cobalt-aluminum-titanium-niobium, nickel-copper, nickel-copper-aluminum-titanium, nickel-molybdenum-chromium-iron, nickel-chromium-molybdenum-copper, nickel-chromium-molybdenum-iron-tungsten-copper, nickel-chromium-molybdenum, and any combination thereof.

The inner feedport 62 is configured to allow a heat transfer fluid to flow into the inner header 60, down through inner tube 72, back up outer tubes 68, 70, into the outer header 64, and back out the outer feedport 66. This flow path through the heat exchanger 58 may also be reversed. Suitable examples of a heat transfer fluid include, but are not limited to mineral oil and other types of oil. The heat exchanger 58 is designed to be substantially immersed in a phase change medium (not shown in this view) and should preferably be manufactured from a material which is compatible with the phase change medium.

Suitable examples of materials which the heat exchanger 58 may be manufactured from include, but are not limited to plain carbon steels; alloy steels, manganese, silicon, silicon-manganese, nickel, nickel-chromium, molybdenum, nickel-molybdenum, chromium, chromium-molybdenum, chromium-molybdenum-cobalt, silicon-molybdenum, manganese-silicon-molybdenum, nickel-chromium-molybdenum, silicon-chromium-molybdenum, manganese-chromium-molybdenum, manganese-silicon-chromium-molybdenum, vanadium, chromium-vanadium, silicon-chromium-vanadium, manganese-silicon-chromium-vanadium, chromium-vanadium-molybdenum, manganese-silicon-chromium-vanadium-molybdenum, chromium-tungsten, chromium-tungsten-molybdenum, chromium-tungsten-vanadium, chromium-vanadium-tungsten-molybdenum, chromium-vanadium-tungsten-cobalt, chromium-vanadium-tungsten-molybdenum-cobalt; stainless steels, austenitic, ferritic, martensitic, duplex, precipitation-hardening, superaustenitic, superferritic; nickel alloys, nickel-chromium-iron, nickel-chromium-iron-aluminum, nickel-chromium-iron-aluminum-titanium, nickel-chromium-iron-aluminum-titanium-niobium, nickel-chromium-iron-cobalt-molybdenum, nickel-chromium-iron-niobium, nickel-chromium-iron-molybdenum-niobium, nickel-chromium-iron-molybdenum-niobium-titanium-aluminum, nickel-chromium-molybdenum-iron-tungsten, nickel-chromium-iron-molybdenum-copper-titanium, nickel-chromium-iron-molybdenum-titanium, nickel-iron-cobalt-aluminum-titanium-niobium, nickel-copper, nickel-copper-aluminum-titanium, nickel-molybdenum-chromium-iron, nickel-chromium-molybdenum-copper, nickel-chromium-molybdenum-iron-tungsten-copper, nickel-chromium-molybdenum, and any combination thereof.

FIG. 5 schematically illustrates a top view of the embodied heat exchanger 58 of FIG. 4. In this embodiment, the outer header 64 has a partial circular shape when viewed from the top. In other embodiments, the shape of the outer header when viewed from the top may include, but is not limited to a complete circle, an oval, a partial oval, a square, a partial square, a rectangle, a partial rectangle, a triangle, a partial triangle, a hexagon, a partial hexagon, and combinations thereof. This top-view shape may be chosen to fit within a design-constrained space or may be chosen to mirror the shape of a structure which will house the heat exchanger 58. In this embodiment, the inner header 60 has a capsule shape when viewed from the top. In other embodiments, the shape of the inner header when viewed from the top may include, but is not limited to a circle, an oval, a square, a rectangle, a loop, a triangle, and a hexagon.

FIG. 6 schematically illustrates a side cross-sectional view of another embodiment of a heat exchanger 74 for use in an energy storage system. The heat exchanger 74 has an inner header 60 with an inner feedport 62. The heat exchanger 74 also has an outer header 64 with an outer feedport 66. The heat exchanger 74 further has a collection header 76 which is fluidically coupled to the inner header 60 via one or more inner tubes 78 and to the outer header 64 via one or more outer tubes 80. The collection header 76 may facilitate the use of a plurality of inner tubes 78 and/or a plurality of outer tubes 80 by providing a common connection point.

In this embodiment, the collection header 76 lies in a plane below the inner header 60 and the outer header 64, but in other embodiments, the collection header 76 could lie in a plane above the inner header 60 and the outer header 64, in a plane above the inner header 60 and below the outer header 64, in a plane below the inner header 60 and above the outer header 64, or in substantially the same plane as the inner header 60 and the outer header 64. Furthermore, although the collection header 76 is illustrated as centered in this embodiment, other embodiments need not be so.

In this embodiment, the collection header 76 has a circular cross-sectional shape. In other embodiments, the inner header and the outer header may have other cross-sectional shapes, such as, but not limited to oval, square, triangular, and hexagonal. Certain cross-sectional shapes may provide more or less surface area for heat transfer or may assist with ease of manufacturing and may be chosen to fit certain heat transfer and assembly goals by those skilled in the art depending on the embodiment.

FIG. 7 schematically illustrates a side cross-sectional view of another embodiment of a heat exchanger 82 for use in an energy storage system. Similar to the embodiment of FIG. 4, the embodiment of FIG. 7 has an inner header 60 having an inner feedport 62 and an outer header 64 having an outer feedport 66, the features of which have been discussed above. The outer header 64 is fluidically coupled to the inner header 60, in this embodiment via outer tubes 84, 86 and inner tube 88. Other embodiments may have differing numbers of inner tubes and/or outer tubes, and may also include a collection header as previously discussed.

As with all of the embodiments of the heat exchangers, this heat exchanger 82 is also designed to be substantially immersed in a phase change medium (not shown in this view). Unlike other thermal energy storage systems which use phase change medium, the current embodiments and their equivalents do not have to maintain the phase change medium in a liquid state because the phase change media is not being pumped anywhere. Instead, the heat exchangers are designed to be immersed in the phase change medium. This offers several benefits, including a simpler, less expensive design and the ability to take advantage of the latent heat of fusion which may still be present in a given phase change medium after it has solidified, thereby increasing the energy storage capacity of thermal energy systems using this design over prior art systems.

One of the considerations when operating a heat exchanger submersed in a phase change medium is how the heat exchanger will initially liquefy the phase change medium. Surprisingly, it has been discovered that if the phase change medium is heated too slowly, there can be too much expansion of the phase change medium because of an insufficient vent path through the phase change medium. This can put undesired stress on a container holding the phase change medium and even cause phase change medium to leak from the container. In order to assist the phase change medium to heat quickly, some embodiments of heat exchangers, such as the heat exchanger 82 in FIG. 7, may have one or more core heat tubes 90 which are directly or indirectly coupled to the inner header 60. Such core heat tubes 90 may trap hot incoming heat transfer fluid supplied to the inner header 60 and create a hot spot within the phase change medium that the exchanger will be placed within. The one or more core heat tubes 90 may be preferably placed near or in the central portion of the heat exchanger to quickly heat the middle of the phase change medium and create a vent path which helps to alleviate outward expansion of the phase change medium.

FIG. 8 schematically illustrates a side cross-sectional view of a further embodiment of a heat exchanger 92 for use in an energy storage system. Similar to the embodiment of FIG. 4, the embodiment of FIG. 8 has an inner header 60 having an inner feedport 62 and an outer header 64 having an outer feedport 66, the features of which have been discussed above. The outer header 64 is fluidically coupled to the inner header 60, in this embodiment via outer tubes 94, 96 and inner tubes 98, 100. Other embodiments may have differing numbers of inner tubes and/or outer tubes, and may also include a collection header as previously discussed. In this embodiment, at least one of the one or more inner tubes 100 has a bypass valve 102 which may be opened or closed by a mechanical, electromechanical, hydraulic, or pneumatic activator. In normal operation, if the bypass valve 102 is opened, the inner tube 100 operates like other inner tubes 98 which do not have a bypass valve, allowing hot heat transfer fluid to flow through. If it is desired to create a hot spot around the inner tubes, however, the bypass valve 102 may be fully or partially closed. As discussed above, the creation of a hot spot can assist the formation of a vent path to alleviate unwanted outward expansion.

FIG. 9 schematically illustrates one embodiment of a thermal energy storage apparatus 104. The thermal energy storage apparatus 104 has a heat exchanger 106 such as the heat exchangers which have been discussed above. The illustrated heat exchanger 106 in FIG. 9 has an inner header 60 having at least one inner feed port 62 and an outer header 64 having at least one outer feed port 66, the features of which have been discussed above. The outer header 64 is fluidically coupled to the inner header 60, in this embodiment via outer tubes 108, 110 and inner tubes 112. Other embodiments may have differing numbers of inner tubes and/or outer tubes, and may also include a collection header and/or one or more core heat tubes and/or one or more inner tubes with a bypass valve as previously discussed. The inner header 60 and the outer header 64 are substantially immersed in a phase change medium 114.

The phase change medium 114 may be selected based on operating temperature considerations. Other considerations for the selection of the phase change medium 114 are chemical stability, non-toxicity, corrosiveness, and thermal properties, such as heat of fusion, thermal conductivity, and heat capacity. Suitable examples of phase change medium 114 may include, but are not limited to salt, a salt mixture, a eutectic salt mixture, lithium nitrate, potassium nitrate, sodium nitrate, sodium nitrite, calcium nitrate, lithium carbonate, potassium carbonate, sodium carbonate, rubidium carbonate, magnesium carbonate, lithium hydroxide, lithium fluoride, beryllium fluoride, potassium fluoride, sodium fluoride, calcium sulfate, barium sulfate, lithium sulfate, lithium chloride, potassium chloride, sodium chloride, iron chloride, tin chloride, zinc chloride, and any combination thereof.

FIG. 10A schematically illustrates a side cross-sectional view of another embodiment of a thermal energy storage apparatus 116. The thermal energy storage apparatus 116 has a heat exchanger 118 similar to the heat exchangers which have been discussed above. The illustrated heat exchanger 118 in FIG. 10A has an inner header 60 having at least one inner feed port 62 and an outer header 64 having at least one outer feed port 66, the features of which have been discussed above. The heat exchanger 118 further has a collection header 76 which is fluidically coupled to the inner header 60 via one or more inner tubes 78 and to the outer header 64 via one or more outer tubes 80. The features of the one or more inner tubes 78, the collection header 76, and the one or more outer tubes 80 have been discussed previously. Other embodiments may have differing numbers of inner tubes and/or outer tubes, and may also include one or more core heat tubes and/or one or more inner tubes with a bypass valve as previously discussed.

The thermal energy storage apparatus 116 also has a tankless structure 120 which is configured to contain the phase change medium 114 such that the inner header 60 and the outer header 64 are substantially immersed in the phase change medium 114. In this embodiment, the tankless structure 120 is constructed of dry-stacked bricks 122. Since the bricks 122 are dry-stacked, they will have inherent small gaps and spaces between them. These spaces 124 have been exaggerated in the drawing to facilitate discussion of the thermal energy storage apparatus 116.

Suitable examples of materials which the bricks 122 may be constructed from include, but are not limited to firebrick, refractory material, castable refractories, refractory brick, mixtures of alumina (Al2O3), silica (SiO2), magnesia (MgO), zirconia (ZrO2), chromium oxide (Cr2O3), iron oxide (Fe2O3), calcium oxide (CaO), silicon carbide (SiC), carbon (C); metallic materials, plain carbon steels; alloy steels, manganese, silicon, silicon-manganese, nickel, nickel-chromium, molybdenum, nickel-molybdenum, chromium, chromium-molybdenum, chromium-molybdenum-cobalt, silicon-molybdenum, manganese-silicon-molybdenum, nickel-chromium-molybdenum, silicon-chromium-molybdenum, manganese-chromium-molybdenum, manganese-silicon-chromium-molybdenum, vanadium, chromium-vanadium, silicon-chromium-vanadium, manganese-silicon-chromium-vanadium, chromium-vanadium-molybdenum, manganese-silicon-chromium-vanadium-molybdenum, chromium-tungsten, chromium-tungsten-molybdenum, chromium-tungsten-vanadium, chromium-vanadium-tungsten-molybdenum, chromium-vanadium-tungsten-cobalt, chromium-vanadium-tungsten-molybdenum-cobalt; stainless steels, austenitic, ferritic, martensitic, duplex, precipitation-hardening, superaustenitic, superferritic; nickel alloys, nickel-chromium-iron, nickel-chromium-iron-aluminum, nickel-chromium-iron-aluminum-titanium, nickel-chromium-iron-aluminum-titanium-niobium, nickel-chromium-iron-cobalt-molybdenum, nickel-chromium-iron-niobium, nickel-chromium-iron-molybdenum-niobium, nickel-chromium-iron-molybdenum-niobium-titanium-aluminum, nickel-chromium-molybdenum-iron-tungsten, nickel-chromium-iron-molybdenum-copper-titanium, nickel-chromium-iron-molybdenum-titanium, nickel-iron-cobalt-aluminum-titanium-niobium, nickel-copper, nickel-copper-aluminum-titanium, nickel-molybdenum-chromium-iron, nickel-chromium-molybdenum-copper, nickel-chromium-molybdenum-iron-tungsten-copper, nickel-chromium-molybdenum, and any combination thereof.

Since the thermal energy storage apparatus 116 has a tankless structure 120, the phase change medium 114 will tend to leak through the gaps 124 in the bricks 122 when it is in a liquid state. For this reason, it is preferred to size the bricks 122 such that they have a cooling zone 126 which encourages the phase change medium 114 to solidify 128 in at least a portion of the gaps 124 defined by the bricks 122. Thus, when the phase change medium 114 is first liquefied, it can seep into the gaps 124 and then cool at some point within the gaps 124 to substantially seal itself 128 to prevent leakage of the phase change medium 114 from the tankless structure 120. The tankless structure 120 does not have the corrosive concerns of typical single or multiple tank systems, it will last longer, it is less expensive to construct, and it is easily scalable. The tankless structure 120 is also suitable for use in seismic regions because it remains flexible due to its dry-stacked and self-sealing nature. Although the illustrated embodiment shows a single layer of bricks 122, other embodiments may utilize multiple layers of bricks 122.

The tankless structure 120 may define a variety of horizontal cross-sectional shapes, such as, but not limited to circular, oval, hexagonal, rectangular, and square. However, since the heat exchanger 118 is configured to take advantage of radial heat differences within the tankless structure 120, a circular horizontal cross-sectional shape defined by the tankless structure 120 is preferred for even heat distribution. A tankless structure 120 which defines a circular horizontal cross-sectional shape will also have reduced mechanical stresses since it will not have corners.

Although the outer header 64 may have many configurations as discussed above, it is preferred that the outer header 64 have a horizontal cross-sectional shape which substantially follows the horizontal cross-sectional shape defined by the tankless structure 120. Such a configuration enables the routing of the outer tubes 80 near to the tankless structure where the temperature of the phase change medium 114 will be at a minimum.

The thermal energy storage apparatus 116 also has a base 130 which supports the tankless structure 120. Although the base 130 is illustrated as being smooth and level, the base 130 in other embodiments may have other profiles. The base 130 may be earth or some structure which is stacked, formed, poured, set, filled or otherwise constructed in place to support the tankless structure 120. Suitable materials for the base 130 include, but are not limited to earth, firebrick, refractory material, concrete, castable refractories, refractory concrete, refractory cement, insulating refractories, gunning mixes, ramming mixes, refractory plastics, refractory brick, mixtures of alumina (Al2O3), silica (SiO2), magnesia (MgO), zirconia (ZrO2), chromium oxide (Cr2O3), iron oxide (Fe2O3), calcium oxide (CaO), silicon carbide (SiC), carbon (C); metallic materials, carbon steels; alloy steels, manganese, silicon, silicon-manganese, nickel, nickel-chromium, molybdenum, nickel-molybdenum, chromium, chromium-molybdenum, chromium-molybdenum-cobalt, silicon-molybdenum, manganese-silicon-molybdenum, nickel-chromium-molybdenum, silicon-chromium-molybdenum, manganese-chromium-molybdenum, manganese-silicon-chromium-molybdenum, vanadium, chromium-vanadium, silicon-chromium-vanadium, manganese-silicon-chromium-vanadium, chromium-vanadium-molybdenum, manganese-silicon-chromium-vanadium-molybdenum, chromium-tungsten, chromium-tungsten-molybdenum, chromium-tungsten-vanadium, chromium-vanadium-tungsten-molybdenum, chromium-vanadium-tungsten-cobalt, chromium-vanadium-tungsten-molybdenum-cobalt; stainless steels, austenitic, ferritic, martensitic, duplex, precipitation-hardening, superaustenitic, superferritic; nickel alloys, nickel-chromium-iron, nickel-chromium-iron-aluminum, nickel-chromium-iron-aluminum-titanium, nickel-chromium-iron-aluminum-titanium-niobium, nickel-chromium-iron-cobalt-molybdenum, nickel-chromium-iron-niobium, nickel-chromium-iron-molybdenum-niobium, nickel-chromium-iron-molybdenum-niobium-titanium-aluminum, nickel-chromium-molybdenum-iron-tungsten, nickel-chromium-iron-molybdenum-copper-titanium, nickel-chromium-iron-molybdenum-titanium, nickel-iron-cobalt-aluminum-titanium-niobium, nickel-copper, nickel-copper-aluminum-titanium, nickel-molybdenum-chromium-iron, nickel-chromium-molybdenum-copper, nickel-chromium-molybdenum-iron-tungsten-copper, nickel-chromium-molybdenum, and any combination thereof.

A support 132 may be provided to support the heat exchanger 118 on the base 130.

FIG. 10B schematically illustrates a side cross-sectional view of a further embodiment of a thermal energy storage apparatus 134. This embodiment of a thermal energy storage apparatus 134 has all the features of the apparatus in FIG. 10A with some added features. At least one layer of insulation 136 may be provided to substantially surround the bricks 122 of the tankless structure 120 thereby helping to reduce heat loss and prolong the energy storage time of the thermal energy storage apparatus 134. Care should be taken that the insulation 136 is not so thick that it prevents the bricks 122 from having a cooling zone 126, otherwise the phase change medium 114 may leak out of the tankless structure 120. Additionally or optionally, a top layer of insulation 138 may be placed over the tankless structure 120. One or more bands 140 may be placed around the tankless structure 120 and the insulation 136 to support the bricks 122.

FIG. 11 illustrates an embodiment of a method for constructing a thermal energy storage system. A base is formed 142. This can include clearing or defining a space on the earth, or it can include forming, laying, pouring, setting, or otherwise building or defining the base on or above a surface. The base may optionally be formed on an insulator. At least one heat exchange system is aligned 144 substantially over the base. The at least one heat exchange system has an inner header and an outer header. Suitable example embodiments of heat exchangers have been discussed herein. A brick wall is dry-laid 146 substantially on the base to surround the at least one heat exchange system or an area where the at least one heat exchange system will be aligned. This takes into account construction methods which first align the heat exchange system over the base and then dry-lay the brick wall around the heat exchange system as well as construction methods which first dry-lay the brick wall and then align the heat exchange system over the base within the brick wall. The area defined by the base and the brick wall are then filled 148 with a phase change medium such that the phase change medium substantially covers the at least one heat exchange system. The brick wall may optionally be insulated 150. The brick wall may optionally be banded 152 for added strength and stability.

Since the thermal energy storage system is a tankless system, the phase change medium may optionally be heated 154 so that it transitions to a liquid phase and enters gaps defined by the dry-laid bricks of the brick wall. Then, the phase change medium may optionally be allowed 156 to cool enough to solidify in at least a portion of the gaps in order to substantially seal the brick wall where it meets the phase change medium.

Another embodiment of a thermal energy storage system 158 is illustrated and discussed with regard to FIGS. 12A-12E. The embodied thermal energy storage system 158, as well as the previously discussed embodiments and their equivalents are designed to be easily scalable from about 50 kilowatt-hours (kWhr) to about 30 MWhr of storage capacity, by way of example. The thermal energy storage system is easily configured to optimize ease of changing fluid temperatures (since this can be different at different installations), phase change medium makeup (since different phase change media have optimum characteristics at the different operating temperatures), and heat transfer fluids (these also vary at installations). Heat exchanger tube spacing, the number of rows, and the number of tubes in each row can be separately adjusted for the outer tubes 160 connecting the outer header 162 to the collection header 164, and the inner tubes 166 connecting the collection header 164 to the inner header 168 to optimize heat transfer, to minimize external heat losses, and to account for thermal conductivity differences between solid phase change media and molten phase change media.

By way of example only, one embodiment of a thermal energy storage system 158 is described below. The design criteria for this thermal energy storage system 158 includes: (1) a phase change medium including a eutectic salt mixture with a melting point a minimum of 75° F. below a maximum oil outlet temperature at the particular solar field the thermal energy storage system 158 is proposed to be used at (This particular field has the lowest operating temperature expected for this thermal energy storage system); (2) a minimum storage capacity of 150 btu/lbm of salt; (3) a minimum storage efficiency of 75%; (4) the ability to transfer 20 btu/lbm of salt when heating the salt and transfer as low as 9 btu/lbm when removing heat from the salt; (5) acceptable material performance for the heat exchange, piping and containment vessel; (6) providing access to the heat exchanger for repairs; (7) an effective containment system for integrity, structural capability and heat retention; (8) a design life of a minimum of 20 years with daily cycles from minimum temperature to maximum temperature; (9) the ability to maintain relatively constant oil (heat transfer fluid) outlet temperature throughout repeated 24 hour cycles; and (10) the ability to utilize the same oil (heat transfer fluid) as the solar field.

The embodied thermal energy storage system 158 includes the containment structure 170 or system, the heat exchanger 172, an oil circulating system, the salt 174 or other phase change media, and an inert gas control system, if required, although the thermal energy storage system 158 could include other types and numbers of components, devices, and systems in other configurations. For example, other embodiments of the thermal energy storage system 158 may include instrumentation to collect data and to control the thermal energy storage system. In some embodiments, the oil circulating system may include a nitrogen overpressure system, a surge tank, (a heater capable of heating the oil to operating temperatures for mock-up purposes only), circulating pump, (a cooler capable of cooling the oil at a constant rate for mock-up purposes only), a bypass throttle valve, reversing valves, and interconnecting piping, although the oil circulating system could include other types and numbers of components, devices, and systems in other configurations.

In this particular example, the thermal energy storage system 158 is using standard heat exchanger sized tubes. In this embodiment, a minimum of four tubes are utilized (two inner tubes 166 and two outer tubes 160), with an OD of ¾″, although the type, number, configuration, and dimensions of these and other tubes or piping, the holes or openings, and the connections throughout can vary. This establishes the minimum size requirement of all components when applying the heat transfer criteria listed above. Additionally the thermal energy storage system 158 is sized to store a minimum of 200 kW-hours of storage, although other amounts of energy could be stored. It is assumed for this particular example that the heat is added to the thermal energy storage system 158 over eight hours, but for sizing it may optionally be assumed that heat is added at a constant rate over 6 hours to account for non-linearity in the heat rate. Therefore, the heat exchanger is sized for a Q of 34 kW, or 0.125 mmbtu/hr, although the heat exchanger could have other sizing for other applications.

As FIGS. 12A, 12B, and 12C illustrate, the heat exchanger 172 comprises a rolled outer header 162, a collection or intermediate header 164, and an inner header 168, although the heat exchanger 172 can comprise other types and numbers of components, devices, and systems in other configurations. The three headers 162, 164, and 168 are connected by tubing sized for the proper heat transfer surface area. The design temperature is 750° F. and design pressure is 250 psig in this particular example, although the thermal energy storage system 172 could be designed for other temperatures, pressures, and characteristics.

The outer header 162 in this embodiment is 3″ nominal piping, 12′ long, rolled on a 22.5″ radius capped on both ends, although the type, number, configuration, and dimensions of these and other tubes or piping, the holes or openings, and the connections throughout can vary. An oil supply inlet (outer feedport) 176 of 1½″ piping enters at the top center of the header. Thirty-eight (38)¾″ outer tubes 160 exit the bottom of the outer header 162 through holes spaced to maintain the tubes parallel to each other, 1¾″ center to center. The outer header 162 is supported solely by the outer tubes 160 and connecting inlet piping 176, and ‘floats’ approximately 1 foot below the top of the salt 174 or other phase change media. A tie-rod may be used to connect the capped ends of the outer header 162. All connections to the outer header 162 are by fillet weld of equal size to the smaller material thickness, although other types of connections could be used.

The collection header 164 is 6″ nominal piping, 4′ long with one end with a bolted flange 178, and the opposite end weld capped 180, although the type, number, configuration, and dimensions of these and other tubes or piping, the holes or openings, and the connections throughout can vary. The collection header 164 is supported on chair legs 182, 6″ off the base 184 of the thermal energy storage system 158, on the approximate centerline of the thermal energy storage system 158. The flanged end 178 butts against one side of the thermal energy storage system 158. Nineteen (19)¾″ holes are located on each side (38 total); located and spaced 1¾″ center to center to accept connecting outer tubes 160 from the outer header 162. At forty-five degrees from the top of the collection header 164 on each side, nineteen (19)¾″ holes spaced 1¾″ center to center are drilled for the inner tubes 166 (total of 38¾″ holes). All tubes are fillet welded to the collection header 164, although other types of connections could be used.

The inner header 168 is 4″ nominal piping, 42″ long, with welded caps on each end, although the type, number, configuration, and dimensions of these and other tubes or piping, the holes or openings, and the connections throughout can vary. Nineteen (19)¾″ holes are located 45 degrees off the bottom center of the inner header 168 in each direction spaced 1¾″ center-to-center (38 holes total) to accept the inner tubes 166 from the collection header 164. A 1½″ oil pipe connection (inner feedport) 186 is provided at the top center of the inner header 168. All tubes are fillet welded to the inner header 168, although other types of connections could be used.

The interconnecting tubes are ¾″ carbon steel tubing, nominal wall thickness of 0.060″, although the number, configuration, and dimensions of these and other tubes or piping and also the holes or openings described throughout can vary. The connecting tubing from the outer header 162 to the collection header 164 is bent to 90 degrees, 35¼″ from one end, 38 total tubes, nineteen per side of the collection header. The connecting tubing from the collection header 164 to the inner header 168 is 35¼″ long, bent at 45 degrees 6″ from one end and 5¼″ from the other end, thirty-eight (38) total. Overall tube length is 271.6 feet or approximately 270 feet for heat transfer purposes.

One embodiment of an oil circulating system (heat transfer fluid circulating system) which can be used with the thermal energy storage system 158 may include a nitrogen overpressure system, surge tank, (heater capable of heating the oil to operating temperatures for testing purposes only), circulating pump, (a cooler capable of cooling the oil at a constant rate for testing purposes only), a bypass throttle valve, reversing valves, and interconnecting piping, although the oil circulating system and each of its components as described herein could include other types and numbers of components, devices, and systems in other configurations. The oil system may be designed for a nominal pumping rate of 20 gpm, a temperature of 750° F. and 250 psig, although the system can be designed for other pumping rates, temperatures, pressures, and other characteristics. The total required volume of oil is approximately 55 gallons plus that required by the field and any turbine heat exchanger configuration coupled to the thermal energy storage system 158. The interconnecting piping is 1½″ carbon steel schedule 40 and is insulated. The throttle bypass valve is a nominal ¾″ valve, with a turndown of 50 and is designed to be controlled by a temperature controller. The intent of this valve is to control downstream temperature at a fixed value. This embodiment of a thermal energy storage system 158 requires four reversing valves which are quarter turn ball valves, although other types of valves can be used. The reversing valves are 1½″ inch nominal. The oil cooler is sized to remove heat from the oil at a maximum rate of 60,000 BTU/our and is air cooled.

Temperature measurements are required on the oil system at the heater inlet and outlet, storage outlet, storage collection header, and cooler inlet and outlet. Four thermocouples will also be embedded in the salt bath. Surface temperatures on the tankless structure can be taken by hand-held instruments. Oil flow through the heater and bypass are required. Oil pressure at the expansion tank, pump discharge, tank inlet and outlet are required.

One of the advantages of the thermal energy storage system 158 is that the containment of the phase change media 174 is tankless. The molten salt 174 is contained in a structure made of refractory 188 (bricks or castable), which contains both the phase change media 174 and the heat exchanger 172.

Unique aspects of this embodiment of a thermal energy storage system 158 include having the inner and outer headers 162, 168 located at the top of the system 158 just below the top of the phase change media 174. This design minimizes the number of penetrations at the molten salt/atmosphere interface where corrosion is a concern. Another unique aspect is that the outer header 162 is a toroid in this embodiment allowing the outer tubes 160 (cooler fluid) to be circumferentially located in close proximity to the tankless structure 170 to minimize heat losses through the exterior of the containment, thereby improving system efficiency. Another unique aspect is that a large diameter intermediate/collection header 164 is located near the bottom of the containment with a flange 178 abutting one wall of the containment structure. This allows the outer tubing 160 to not only be located near the outer wall (as described above), but also to be located near the bottom of the containment to minimize heat losses through the base 184. The collection header 164 design also allows for ease of serviceability of the heat exchanger because it can be accessed without removal of the majority of the phase change media 174 by removing nearby bricks 188 and burrowing in to the flange 178.

Additionally, this design improves mixing of the fluid phase change medium 174 to promote thermal consistency. Differing designs between inner outer tubing to account for differences in heat transfer characteristics between the phase change media in the upper center of the containment from the periphery.

Another advantage of this embodiment of a thermal energy storage system 158 is that it may be designed with a valve control system including both reversing valves and temperature control valves. The reversing valves allow for flow to enter the heat exchange system 172 through the inner header 168 (See FIG. 12D) when heating the phase change media 174, and conversely to enter the heat exchanger 172 through the outer header 162 (See FIG. 12E) when cooling the system. This keeps the cooler oil (heat transfer fluid) always on the outside of the containment, minimizing heat losses through the exterior. The constant temperature control valves maintain oil temperature to the turbine supply heat exchanger to operate at a constant temperature whether or not the thermal energy storage system is being heated or cooled (i.e. energy added or removed). This allows a turbine to be designed to operate at peak efficiency because a single inlet condition is maintained.

FIG. 13 schematically illustrates an embodiment of a thermal energy power system 190. The thermal energy power system 190 has a thermal energy storage apparatus 116, the features of which have been discussed above with regard to FIG. 10A. Other embodiments of thermal energy power systems may have other embodiments of thermal energy storage apparati as have also been discussed above with numerous examples and their equivalents. The thermal energy power system 190 has at least one inner valve 192 which may be used to selectably and fluidically couple the inner header 60 to either a renewable heat source 194 or a pump 196. Suitable examples of a renewable heat source 194 include, but are not limited to solar cells, solar mirror arrays, and wind turbines. Other non-limiting examples of renewable heat sources 194 may include industrial stack heat and/or excess heat which is the by-product of industrial, municipal, institutional, individual, or other activity. For example, a manufacturing plant which operates during the day may generate heat which can be stored to supply power for other activities at a later time. Heat transfer fluid is preferably used to remove heat from the renewable heat source 194 and transfer it throughout the system when moved by the pump 196. The thermal energy power system 190 also has at least one outer valve 198 which may be used to selectably and fluidically couple the outer header 64 to either the renewable heat source 194 or the pump 196. The inner header 60 and the outer header 64 are reversibly connected in a closed loop with the pump 196, the renewable heat source 194, and a turbine plant 200. The reversible connection can be made possible by a variety of valve devices, the illustrated inner and outer selection valves 192, 198 being only one example. The turbine plant 200 uses heat delivered to it by the pump from the renewable heat source 194 or the thermal energy storage apparatus 116 to generate steam which drives generators to make electricity.

FIG. 14 schematically illustrates flow through the embodied thermal energy power system of FIG. 13 during a heating mode. During this heating mode, the renewable energy source 194 is available (producing heat), for example, when the sun is shining on a solar array. The inner selection valve 192 is set to a first position (position A in the drawing) which couples heated heat transfer fluid 202 from the renewable heat source 194 to the inner header 60 of the thermal energy storage apparatus 116. The outer selection valve 198 is set to a second position (position B in the drawing) which fluidically couples the outer header 64 to the turbine plant 200. In this embodiment, the pump 196 is in the fluid path from the outer header 64 to the turbine plant 200 to provide the force to move the thermal transfer fluid through the power system. Other embodiments may place the pump in different locations or use more than one pump. Thermal transfer fluid from the turbine plant 200 is then coupled back to the renewable heat source 194.

During operation, the heat transfer fluid 202 which is heated by the renewable heat source passes into 204 the inner header and down 206 through one or more inner tubes within the approximate center of the phase change media. Heat from the heat transfer fluid is transferred to and stored by the phase change media. The heat transfer fluid then passes 208 through the collection header, up the one or more outer tubes, and into the outer header. The heat transfer fluid, having given-up some of its heat to the phase change media may then be pushed 210 to the turbine plant 200 if it still has enough heat to generate steam. Alternatively, the heat transfer fluid may be routed back to the renewable heat source or augmented with a separate line of hot heat transfer fluid from the renewable heat source before being sent to the turbine plant. The cooled heat transfer fluid leaving the turbine plant is returned 212 to the renewable heat source for further heating.

FIG. 15 schematically illustrates flow through the embodied thermal energy power system of FIG. 13 during a cooling mode. During this cooling mode, the renewable energy source 194 is not available (not producing heat), for example, when the sun is not shining on a solar array. The outer selection valve 198 is set to a first position (position A in the drawing) which fluidically couples the outer header 64 to the renewable heat source which is currently not generating heat. The inner selection valve 192 is set to a second position (position B in the drawing) which couples heated heat transfer fluid (heated by the phase change media 114) from the inner header 60 of the thermal energy storage apparatus 116 to the to the turbine plant 200. In this embodiment, the pump 196 is in the fluid path from the inner header 60 to the turbine plant 200 to provide the force to move the thermal transfer fluid through the power system. Other embodiments may have the pump in different locations or use more than one pump. Thermal transfer fluid from the turbine plant 200 is then coupled back to the renewable heat source 194.

During operation, the heat transfer fluid which is heated by the phase change medium passes 214 from the collection header up into the inner header and is pushed 216 to the turbine plant for generating steam. The heat transfer fluid is cooled after leaving the turbine plant and is recirculated 218 back to the renewable heat source (which is currently not producing heat). The heat transfer fluid is then moved 220 into the outer header and down 222 through the one or more outer tubes and back into the collection header where the heat transfer fluid may be heated again to power the turbine plant. In alternate embodiments, the cooled heat transfer fluid which leaves the turbine plant may be routed to circumvent the renewable heat source, which is not producing heat, directly back into the outer header.

FIG. 16 illustrates an embodiment of a method for controlling a thermal energy storage system. A determination is made 224 as to whether a renewable heat source is available. When a renewable heat source is available 226: i) the renewable heat source is thermally and fluidically coupled 228 to an inner header of a heat exchange system which is substantially immersed in a phase change medium and which is further coupled to an outer header of the heat exchange system which is also substantially immersed in the phase change medium; and ii) the outer header is thermally and fluidically coupled 230 to a turbine plant and then back to the renewable heat source in a closed-loop heating mode which provides a remaining renewable energy source heat to the turbine plant. When the renewable heat source is not available 232: i) the renewable heat source is thermally and fluidically coupled 234 to the outer header; and ii) the inner header is thermally and fluidically coupled 236 to the turbine plant and then back to the renewable heat source in a closed-loop cooling mode which provides a stored heat to the turbine plant.

Having thus described several embodiments of the claimed invention, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and the scope of the claimed invention. Additionally, the recited order of the processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes to any order except as may be specified in the claims. Accordingly, the claimed invention is limited only by the following claims and equivalents thereto. 

1. A thermal energy storage apparatus, comprising: a phase change medium; an inner header having at least one inner feed port; an outer header having at least one outer feed port and fluidically coupled to the inner header; and wherein the inner header and the outer header are configured to be substantially immersed in the phase change medium.
 2. The thermal energy storage apparatus of claim 1, wherein the phase change medium is selected from the group consisting of a salt, a salt mixture, a eutectic salt mixture, lithium nitrate, potassium nitrate, sodium nitrate, sodium nitrite, calcium nitrate, lithium carbonate, potassium carbonate, sodium carbonate, rubidium carbonate, magnesium carbonate, lithium hydroxide, lithium fluoride, beryllium fluoride, potassium fluoride, sodium fluoride, calcium sulfate, barium sulfate, lithium sulfate, lithium chloride, potassium chloride, sodium chloride, iron chloride, tin chloride, and zinc chloride.
 3. The thermal energy storage apparatus of claim 1, wherein the inner header is centered within the outer header.
 4. The thermal energy storage apparatus of claim 1, wherein the inner header and the outer header lie on substantially the same plane.
 5. The thermal energy storage apparatus of claim 1, further comprising a collection header, and wherein the inner header is fluidically coupled to the outer header via the collection header.
 6. The thermal energy storage apparatus of claim 5, further comprising: one or more inner tubes coupled between the inner header and the collection header; one or more outer tubes coupled between the outer header and the collection header; and wherein the inner header is fluidically coupled to the outer header via the one or more inner tubes, the collection header, and the one or more outer tubes.
 7. The thermal energy storage apparatus of claim 6, further comprising one or more core heat tubes coupled to the inner header.
 8. The thermal energy storage apparatus of claim 6, wherein at least one of the one or more inner tubes further comprise a bypass valve configured to selectably create a hot spot in the phase change medium.
 9. The thermal energy storage apparatus of claim 6, further comprising a tankless structure configured to contain the phase change medium such that the inner header and the outer header are substantially immersed in the phase change medium.
 10. The thermal energy storage apparatus of claim 9, wherein the tankless structure comprises bricks.
 11. The thermal energy storage apparatus of claim 10, wherein the bricks comprise a material selected from the group consisting of firebrick, refractory material, castable refractories, refractory brick, mixtures of alumina (Al2O3), silica (SiO2), magnesia (MgO), zirconia (ZrO2), chromium oxide (Cr2O3), iron oxide (Fe2O3), calcium oxide (CaO), silicon carbide (SiC), carbon (C); metallic materials, plain carbon steels; alloy steels, manganese, silicon, silicon-manganese, nickel, nickel-chromium, molybdenum, nickel-molybdenum, chromium, chromium-molybdenum, chromium-molybdenum-cobalt, silicon-molybdenum, manganese-silicon-molybdenum, nickel-chromium-molybdenum, silicon-chromium-molybdenum, manganese-chromium-molybdenum, manganese-silicon-chromium-molybdenum, vanadium, chromium-vanadium, silicon-chromium-vanadium, manganese-silicon-chromium-vanadium, chromium-vanadium-molybdenum, manganese-silicon-chromium-vanadium-molybdenum, chromium-tungsten, chromium-tungsten-molybdenum, chromium-tungsten-vanadium, chromium-vanadium-tungsten-molybdenum, chromium-vanadium-tungsten-cobalt, chromium-vanadium-tungsten-molybdenum-cobalt; stainless steels, austenitic, ferritic, martensitic, duplex, precipitation-hardening, superaustenitic, superferritic; nickel alloys, nickel-chromium-iron, nickel-chromium-iron-aluminum, nickel-chromium-iron-aluminum-titanium, nickel-chromium-iron-aluminum-titanium-niobium, nickel-chromium-iron-cobalt-molybdenum, nickel-chromium-iron-niobium, nickel-chromium-iron-molybdenum-niobium, nickel-chromium-iron-molybdenum-niobium-titanium-aluminum, nickel-chromium-molybdenum-iron-tungsten, nickel-chromium-iron-molybdenum-copper-titanium, nickel-chromium-iron-molybdenum-titanium, nickel-iron-cobalt-aluminum-titanium-niobium, nickel-copper, nickel-copper-aluminum-titanium, nickel-molybdenum-chromium-iron, nickel-chromium-molybdenum-copper, nickel-chromium-molybdenum-iron-tungsten-copper, and nickel-chromium-molybdenum.
 12. The thermal energy storage apparatus of claim 10, further comprising at least one layer of insulation substantially surrounding the bricks.
 13. The thermal energy storage apparatus of claim 12, further comprising at least one band supporting the bricks.
 14. The thermal energy storage apparatus of claim 10, wherein the bricks are configured to have a cooling zone which encourages the phase change medium to solidify in at least a portion of gaps defined by the bricks.
 15. The thermal energy storage apparatus of claim 9, further comprising a base which supports the tankless structure.
 16. The thermal energy storage apparatus of claim 15, wherein the base comprises a material selected from the group consisting of earth, firebrick, refractory material, concrete, castable refractories, refractory concrete, refractory cement, insulating refractories, gunning mixes, ramming mixes, refractory plastics, refractory brick, mixtures of alumina (Al2O3), silica (SiO2), magnesia (MgO), zirconia (ZrO2), chromium oxide (Cr2O3), iron oxide (Fe2O3), calcium oxide (CaO), silicon carbide (SiC), carbon (C); metallic materials, carbon steels; alloy steels, manganese, silicon, silicon-manganese, nickel, nickel-chromium, molybdenum, nickel-molybdenum, chromium, chromium-molybdenum, chromium-molybdenum-cobalt, silicon-molybdenum, manganese-silicon-molybdenum, nickel-chromium-molybdenum, silicon-chromium-molybdenum, manganese-chromium-molybdenum, manganese-silicon-chromium-molybdenum, vanadium, chromium-vanadium, silicon-chromium-vanadium, manganese-silicon-chromium-vanadium, chromium-vanadium-molybdenum, manganese-silicon-chromium-vanadium-molybdenum, chromium-tungsten, chromium-tungsten-molybdenum, chromium-tungsten-vanadium, chromium-vanadium-tungsten-molybdenum, chromium-vanadium-tungsten-cobalt, chromium-vanadium-tungsten-molybdenum-cobalt; stainless steels, austenitic, ferritic, martensitic, duplex, precipitation-hardening, superaustenitic, superferritic; nickel alloys, nickel-chromium-iron, nickel-chromium-iron-aluminum, nickel-chromium-iron-aluminum-titanium, nickel-chromium-iron-aluminum-titanium-niobium, nickel-chromium-iron-cobalt-molybdenum, nickel-chromium-iron-niobium, nickel-chromium-iron-molybdenum-niobium, nickel-chromium-iron-molybdenum-niobium-titanium-aluminum, nickel-chromium-molybdenum-iron-tungsten, nickel-chromium-iron-molybdenum-copper-titanium, nickel-chromium-iron-molybdenum-titanium, nickel-iron-cobalt-aluminum-titanium-niobium, nickel-copper, nickel-copper-aluminum-titanium, nickel-molybdenum-chromium-iron, nickel-chromium-molybdenum-copper, nickel-chromium-molybdenum-iron-tungsten-copper, and nickel-chromium-molybdenum.
 17. The thermal energy storage apparatus of claim 9, wherein the outer header has a shape which substantially follows a shape defined by the tankless structure.
 18. The thermal energy storage apparatus of claim 9, wherein the tankless structure defines a horizontal cross-sectional shape which is selected from the group consisting of circular, oval, hexagonal, rectangular, and square.
 19. The thermal energy storage apparatus of claim 1, further comprising: at least one inner valve; at least one outer valve; an inner pipe which couples the inner valve to the inner feed port; and an outer pipe which couples the outer valve to the outer feed port.
 20. The thermal energy storage apparatus of claim 19, wherein the inner pipe and the outer pipe enter the phase change medium substantially vertically.
 21. The thermal energy storage apparatus of claim 19, wherein the inner pipe and the outer pipe enter the phase change medium substantially horizontally.
 22. The thermal energy storage apparatus of claim 1, wherein the inner header and the outer header comprise material selected from the group consisting of plain carbon steels; alloy steels, manganese, silicon, silicon-manganese, nickel, nickel-chromium, molybdenum, nickel-molybdenum, chromium, chromium-molybdenum, chromium-molybdenum-cobalt, silicon-molybdenum, manganese-silicon-molybdenum, nickel-chromium-molybdenum, silicon-chromium-molybdenum, manganese-chromium-molybdenum, manganese-silicon-chromium-molybdenum, vanadium, chromium-vanadium, silicon-chromium-vanadium, manganese-silicon-chromium-vanadium, chromium-vanadium-molybdenum, manganese-silicon-chromium-vanadium-molybdenum, chromium-tungsten, chromium-tungsten-molybdenum, chromium-tungsten-vanadium, chromium-vanadium-tungsten-molybdenum, chromium-vanadium-tungsten-cobalt, chromium-vanadium-tungsten-molybdenum-cobalt; stainless steels, austenitic, ferritic, martensitic, duplex, precipitation-hardening, superaustenitic, superferritic; nickel alloys, nickel-chromium-iron, nickel-chromium-iron-aluminum, nickel-chromium-iron-aluminum-titanium, nickel-chromium-iron-aluminum-titanium-niobium, nickel-chromium-iron-cobalt-molybdenum, nickel-chromium-iron-niobium, nickel-chromium-iron-molybdenum-niobium, nickel-chromium-iron-molybdenum-niobium-titanium-aluminum, nickel-chromium-molybdenum-iron-tungsten, nickel-chromium-iron-molybdenum-copper-titanium, nickel-chromium-iron-molybdenum-titanium, nickel-iron-cobalt-aluminum-titanium-niobium, nickel-copper, nickel-copper-aluminum-titanium, nickel-molybdenum-chromium-iron, nickel-chromium-molybdenum-copper, nickel-chromium-molybdenum-iron-tungsten-copper, and nickel-chromium-molybdenum.
 23. A thermal energy power system, comprising: a) a phase change medium; b) an inner header; c) an outer header; d) a collection header; e) one or more inner tubes coupled between the inner header and the collection header; f) one or more outer tubes coupled between the outer header and the collection header, wherein the inner header is fluidically coupled to the outer header via the one or more inner tubes, the collection header, and the one or more outer tubes; g) a brick structure configured to contain the phase change medium such that the inner header and the outer header are substantially immersed in the phase change medium and wherein the bricks are configured to have a cooling zone which encourages the phase change medium to solidify in gaps defined by the bricks h) a base which supports the brick structure; i) a pump; j) a renewable heat source; k) a turbine plant; and l) wherein the inner header and the outer header are reversibly connected in a closed loop with the pump, the renewable heat source, and the turbine plant and wherein the closed loop carries a heat transfer fluid.
 24. The thermal energy power system of claim 23, wherein the renewable heat source is selected from the group consisting of a solar parabolic mirror, a solar mirror farm, and a wind turbine.
 25. The thermal energy power system of claim 23, wherein the heat transfer fluid comprises oil.
 26. A method of constructing a thermal energy storage system, comprising: forming a base; aligning at least one heat exchange system substantially over the base, the at least one heat exchange system comprising an inner header and an outer header; dry-laying a brick wall substantially on the base to surround the at least one heat exchange system or an area where the at least one heat exchange system will be aligned; and filling the area defined by the base and the brick wall with a phase change medium such that the phase change medium substantially covers the at least one heat exchange system.
 27. The method of claim 26, wherein forming the base further comprises forming the base on an insulator.
 28. The method of claim 26, wherein the brick wall comprises a material selected from the group consisting of firebrick and refractory brick.
 29. The method of claim 26, further comprising insulating the brick wall.
 30. The method of claim 26, further comprising banding the brick wall.
 31. The method of claim 26, further comprising: heating the phase change medium so that it transitions to a liquid phase and enters gaps defined by the dry-laid bricks of the brick wall; and allowing the phase change medium to cool enough to solidify in at least a portion of the gaps in order to substantially seal the brick wall where it meets the phase change medium.
 32. A method of controlling a thermal energy storage system, comprising: a) when a renewable heat source is available: i) thermally and fluidically coupling the renewable heat source to an inner header of a heat exchange system which is substantially immersed in a phase change medium and which is further coupled to an outer header of the heat exchange system which is also substantially immersed in the phase change medium; and ii) thermally and fluidically coupling the outer header to a turbine plant and then back to the renewable heat source in a closed-loop heating mode which provides a remaining renewable energy source heat to the turbine plant; and b) when the renewable heat source is not available: i) thermally and fluidically coupling the renewable heat source to the outer header; and ii) thermally and fluidically coupling the inner header to the turbine plant and then back to the renewable heat source in a closed-loop cooling mode which provides a stored heat to the turbine plant.
 33. A heat exchanger for a thermal energy storage system, comprising: an inner header having at least one inner feedport; an outer header having at least one outer feedport and fluidically coupled to the inner header; and wherein the inner and outer feedports are configured to enable a heat transfer fluid to reversibly flow from the inner header to the outer header when the inner header and the outer header are substantially immersed in a phase change medium.
 34. The heat exchanger of claim 33, wherein the inner header is centered within the outer header.
 35. The heat exchanger of claim 33, wherein the inner header and the outer header lie on substantially the same plane.
 36. The heat exchanger of claim 33, further comprising a collection header, and wherein the inner header is fluidically coupled to the outer header via the collection header.
 37. The heat exchanger of claim 36, further comprising: one or more inner tubes coupled between the inner header and the collection header; one or more outer tubes coupled between the outer header and the collection header; and wherein the inner header is fluidically coupled to the outer header via the one or more inner tubes, the collection header, and the one or more outer tubes.
 38. The heat exchanger of claim 37, further comprising one or more core heat tubes coupled to the inner header.
 39. The heat exchanger of claim 37, wherein at least one of the one or more inner tubes further comprises a bypass valve. 